ge.) Still other people prefer one, especially if it's going to be displayed in their home, that does not look like an urn. 
What are they and are they required? Almost every cemetery requires a vault to bury a casket; fewer require one to bury an urn. A burial vault is a protective outer container that protects the urn and also maintains the integrity of the grave. Its structure protects the urn from the elements in the ground and also from the common use of heavy equipment in digging other graves in cthe area. It maintains the appearance of the grave as there is less settling of the ground on top of a solid structure, the vault. Another less obvious advantage of an urn vault is that it keeps the ashes in their unaltered state so that if they are ever to be moved to a different grave, it can be done easily. Urn vaults are most commonly made from concrete but there are also items that are a combination of an urn and an urn vault. Almost all cemeteries will accept these. They are usually made from a type of molded plastic or marble.
Concrete urn vaults are available with or without a protective lining. Those with a lining also have a seal to help protect the urn from moisture and elements in the ground. For extra protection, some even provide additional protection by being double or triple reinforced. One of the manufacturers has a website with pictures and illustrations to help explain this. www.wilbertonline.com/store/index.asp?DEPARTMENT_ID=34